The present invention is related to an air-to-fuel ratio feedback control system, and more particularly to a system wherein air-fuel mixture is controlled as desired during specific operating conditions of engine.
Various types of air-to-fuel ratio feedback control system in which air-fuel mixture is controlled to the stoichiometric mixture in response to the oxygen concentration in exhaust gases are known well in the art. One exemplary system is disclosed in the U.S. Pat. No. 3,745,768 in which air and/or fuel of air-fuel mixture are/is feedback-controlled in response to the oxygen concentration. Another exemplary system is disclosed in the U.S. Pat. No. 3,916,170 in which the air-fuel mixture is corrected in proportion to the difference between integrator output level and a preset constant level so that the air or the fuel is increased or decreased. These feedback control system has a disadvantage in that the air-fuel mixture is constantly kept at the stoichiometric mixture contrary to such a requirement as that richer or leaner mixture than the stoichiometric mixture must be supplied to an engine during respective heavy load such as accelerating or no load such as decelerating condition.